Blast Freezer Unit causing liquid line vibration below -37 deg C Evap Temp

[thejus123]

We are working on a Blast Freezer Unit in Dubai

Unit Selection
Frascold 30 HP Double Stage (SA 30 102 51-Z-Y/4) with Liquid Subcooler (19.5 kW @ -46 C Evap Temp, 43 C Amb, R404a)
LU-VE FF63H261E12 Evaporator (19.6 kW @ -40 C Air Inlet, -46 C Evap Temp, R404a)
Suction Line Size - 2 1/8", Liquid Line Size - 7/8"
Danfoss Expansion Valve - TES20 Orifice 9 with MOP30/-20 C ( 22 kW @ -46 C, 53 Cond)

Standard Subcooling kit with TES 2 Orifice 5 Exp Valve/Liquid Injection Valve.

Parameters -30 deg C Room Temp, 5 psi(g) Suction Pressure, 400 psi(g) discharge pressure, 20 A Motor Amps
(Ambient Temp : 43 deg C)

Problems Faced
1) The Compressor is not cooled by sub cooler even at 0 deg C Evaporation.
2) Hissing sound from the liquid line
3) Heavy Vibration in the liquid line side on dropping below -30 deg C Room Temp and has to be switched off to avoid damage to the liquid line distributors to evaporator.
4) The Suction pressure guage is not dropping down uniformly. Sometime the guage pressure increases while the room temperature is decreasing and then coming down.

What would be the possible causes? Has anyone experienced such a case?

Looking forward to your advices.

We are planning for a complete vacuuming of the system and charge of new refrigerant (Frascold says only 11 kg charge for its unit- Is it enough?) to bring down the possibility of system moisture.

Any other concern?

[Magoo]

Discharge pressure too high at 27 bar 400psig, high velocity liquid vapour in liquid line causing noise and vibration, suction pressure fluctuating as MOP TXVs try to regulate, high suction super heat due to lack of liquid at TX valve and high evap super heat. System over performing during pull down, install a crankcase pressure regulating valve and allow compressor to operate within design envelope. Check sight glass in liquid line, it should clear as system gets closer to design temps in room,

[Magoo]

It is critical to keep compounded recip compressor with in design, otherwise it will overheat and fail. The interstage velocities will be too high and minimal interstage sub cooling, creating more heat in high stage and super high discharge SDT conditions, and risk blowing a safety relief valve. With a 2 1/8" suction you need a Danfoss PM crankcase reg a pilot controller. Keep SST at compressor at around -20' C, and SDT at around +40' C

[thejus123]

Thanks Magoo for your reply. So you recommend to add a crank case regulator with pilot control?
The range KVL is available only upto 1 3/8" and for bigger systems Danfoss Recommend ICS valves with Pilot Control. (ICS1-50 -027H5023).

Are there any other concern.
We doubt the performance of sub cooler, the temperature in the liquid line from receiver is reduced by only 5 degrees by the sub cooler to evaporator. (43 C/ 38 C)
Also the receiver is sized only at 18 litres designed for a charge of only 10 kg refrigerant which is very low for such a system. (20 kW @ -46 C ).
Just need to be sure if there are other concerns affecting the issue before making changes in the system.

[Magoo]

once you get the suction pressure down with in compressor limits the vapour volume circulated will drop as well and velocities through condenser will drop, and improve sub cooling at condenser. The liquid receiver needs only a liquid seal to operate correctly and is there for pump down storage for servicing, seems to be small at 10kg/18 litres capacity. At low temp design conditions the evaporator will hold quite an amount of liquid, add liquid line volume.

[moideen]

Hi, thejus,
Have you checked your 404a refrigerant? In Dubai and sharjah the duplicates are available. First of all ensure the quality of refrigerant. And provide more info , such as In/out condenser air temperature, In/out evaporator air temperature, Superheat of evaporator and suction, Discharge line temperature, Compressor temperature of barrel, underside of all head, discharge head, Subcooling, Length of liquid line …….etc.then you may get more replay from RE experts like magoo.

[thejus123]

We used honeywell US refrigerant from reputed distributor.

[thejus123]

The system however was working better with a smaller expansion valve. (TES 5 Orifice 3) Theoretically it should not be possible but practically it was achieving -40 C in the room without vibrations.
We are not really satisfied, but the client was persisting to start the facility.

[monkey spanners]

Is the liquid line too small?

[moideen]

Is the liquid line too small?

hi,ms,its already mentioned Suction Line Size - 2 1/8", Liquid Line Size - 7/8"

[monkey spanners]

hi,ms,its already mentioned Suction Line Size - 2 1/8", Liquid Line Size - 7/8"

Thanks Moideen, yes i saw that but i don't have enough experience on equipment this size to know just from the sizes and duty if the pipes are sized correctly, so thought i would ask the question (and also prompt the original poster to double check their sizing)

[install monkey]

hissing sound on the liq line indicates a restriction, check for a temperature difference accross the liq drier,also is there a gauze in the tev orifice clogging, condenser coil clean,all fans operating ok, as 46deg ambient is high.
is the rejected condenser air short cycling?